Steel



Patented Aug. 22, 1944 Bethlehem Steel Company,

Pennsylvania a. corporation 01' No Drawing. Application February 28,1942, Serial No. 432,796

4 Claims. (Cl. 75-123) My invention relates to rimmed steels, and, moreparticularly, it relates to rimmed steels having non-agingcharacteristics.

It has been known for some times that steels could be prepared havingnon-aging characteristics by'subjecting them, while in the liquid state,to the action of strongly deoxidizing substances, such as aluminum,titanium, and zirconium, these elements being used in amounts sufiicientto efiect substantially complete deoxidation, i. e., to 'fully "kill"the steel.

Rimming steels, as is well known, are efiervescing steels which boil"actively in the mold after pouring. This boiling is caused by thevigorous evolution of C gas due to the reaction between carbon and theiron oxide in the steel. Obviously, rimming steels are markedlydifferent from killed steels, in that killed steels (especially whenfully killed to make them non-aging) contain little, if any, oxide,while rimming steels must contain considerable oxide to produce theboiling action just referred to.

As is well known, there are certain definite advantages in producing arimming steel instead of a killed steel. For one thing, there isconsiderably less pipe in rimmed steel than in killed steel, an ingot ofrimmed steel therefore requiring less cropping than does killed steel.Prior to my invention, however, rimmed steels have not been non-aging.

I have discovered that by the use of substances which combine readilywith nitrogen but which do not act as strong deoxidizers I can rendersteels non-aging without killing. Ihave found that vanadium isparticularly advantageous in this respect as, when added in particularamounts to a r g steel, the steel is rendered nonaging withoutinterfering with the rimming action. As will appear later, the additionof vanadium not only produces a non-aging, rimmed steel, but alsocontributes other advantageous properties. My invention, therefore,comprises the addition of vanadium or equivalent substance to rimmingsteel whereby the steel is rendered non-aging without losing thecharacteristics and advantages of rimming steel.

In describing my invention, I shall first give, as an illustration, theuse of vanadium. In preparing my steel, the steel is refined in thefurthe use of strongly oxidizing conditions thereby sumciently low incarbon, say, of the order of .07%, and with a very low silicon contentwhich ordinarily will be below .0l%. In accordance with standard rimmingpractices, deoxidizers, such as aluminum, manganese and silicon, areadded, if necessary, to the ladle or to the mold to control the rimmingaction.

To the steel in the ladle or in the mold I add vanadium in amountsumcient to give the steel a vanadium content of from .01% to .15%. Thevanadium may be introduced in any suitable form. For example, I havefound it very effective to add vanadium as the standard grade of 40%ferro-vanadium. The vanadium may also be introduced as vanadiumpent-oxide or as sodium or calcium vanadate. Better recoveries areobtained when using ferro-vanadium than when using compounds such asvanadium oxide, 1. e., a greater percentage of the vanadium addedbecomes a constituent of the final product. When adding vanadium in theform of ferro-vanadium, recoveries range from 60% to as high as of thevanadium added. When using vanadium oxide, V205, recoveries may beobtained close to 50%.

Preferably the vanadium, regardless of the form in which it is used, isadded to the ladle during tapping of the heat or to the molds duringpouring of the ingots. In adding vanadium to the ladle better recoveryof vanadium is secured if it is added after the farm-manganese and afterthe addition of small amounts of aluminum or silico-manganese whichlatter are used to help to control the degree of rimming action. In somecases it is more emcient to add a portion of the vanadium to the ladleduring tapping and a portion to the molds during pouring of the ingots.

I have found that a very high degree of resistance to age-hardening isobtained when the rimmed. steel has a content of .03% vanadium orgreater, up to .15%. For example, by adding one pound of vanadium in theform of 40% ferrovanadium, to the ladle the resulting steel containsabout .03% of vanadium. Such a steel, when tested, shows non-aging chaacteristics equal to those of fully aluminum killed steel. Yet suchsteel has all the essential characteristics of rimmed steel, and all ofthe procedural advantages of rimming tested at different temperaturesfor tensile strength a sample of this steel gave the following results:

Tensile strength, lbs. per sq. in.

Tested at 400 Chan e F. g

li/ton V in ladle as 407 [6110- Per cent vanadium -1 .032 44, 900

To those skilled in the art it is obvious that the decided decrease intensile strength from room temperature to 400 F. indicates this steel tohave excellent non-aging characteristics. When a sheet oi steel Preparedfrom this steel was as sheet for operations elongation, and agedskin-passed to about 1% the following results at 212 1'. for 24 hours,were obtained:

This shows clearly the excellence of this material as regards itsnon-aging properties.

My ,steel has excellent properties when used involving deep drawing.Sheet material can be made of my steel in the regular way, involving theusual rolling operations and annealing, and then, if desired forparticular purposes, it can be deep drawn. My

steel has a particularly satisfactory structure for l the deep drawingoperation. It has a fine grain near the surface and a somewhat coarsergrain in the interior. This condition is the reverse of that in ordinaryrimmed steel sheet and renders the material particularly adapted fordeep drawing. In this connection, it is to be'pointed out that rimmedsteel sheet has a better surface than that of killed steel. In myvanadium-containing rimmed steel, the surfaces of sheets were noticeablysmoother, and with fewer defects, than the surface of non-aging fullykilled steel sheets.

Although, as I have pointed out, ahigh degree of non-agingcharacteristics can be obtained when rimmed steel contains from .03% to.15% of vanadium, it is not always essential that steels possess such ahigh degree of non-aging, Therefore, I find it feasible, for certainpurposes, to introduce smaller amounts of vanadium, getting a lesserdegree or non-aging but still sufflcient for certain purposes. Forexample, I may add from one-quarter to three-quarters of a pound of 40%vanadium for each ton of steel and thereby lessen the aging tendenciesth necessary degree for many purposes. In contrast with this conditionof partially overcoming the aging tendencies by adding vanadium torimming steels, we have the condition in killed steels that it isessential that the steel be completely killed. The minimum amount ofvanadium used in my invention, however, should be such as not to give avanadium content in the steel substantially less than .01 Obviously, myinvention is not limited to the manufacture of sheet steel, although itis very advantageous in that application. All kinds of rimmed steel, ofvarying carbon contents, may be made non-aging in the way described. Inrimmed steel the surface is lower in carbon that the interior and thesurface is therefore softer. Thus my vanadium-containing rimmed steel isadvantageously used in firebox steels, boiler steels, structural steelsto be galvanized, etc., these steels being less liable to brittlenessand cracking in bending and other types of deformation than withnon-aging killed steels.

While I have found vanadium to be particularly advantageous as anaddition to rimmed steel, I may also use other materials which areeffective to combine with nitrogen in the steel but which do not act asstrong deoxidizers. For example, I may use chromium which combinesfairly readily with nitrogen but which, at the same time, is a milddeoxidizer. chromium may be used of the order of .3%, giving aneffectively rimming steel with substantial non-aging characteristics.After suitable annealing, sheet made of this steel is sufficiently softfor satisfactory deep drawing.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent is:

1. A steel having the characteristics due to rimming, containingvanadium between .01% and .15%, said steel having non-agingcharacteristics.

2. A steel having the characteristics due to rimming, containingvanadium between .03% and .10%, said steel having non-agingcharacteristics.

3. A steel having the characteristics due to rimming, containingvanadium between .01% and .15%.

4. A deep drawing sheet steel having the characteristics due to rimmingand annealing. containing vanadium between .0l% and .15%.

SAMUEL Amounts of

